Gas ignition products are well known and needed types of product. In such products typically an electrically controlled relay controls the opening of a valve in the gas line, which supplies gas to the gas burner. When it is desired to supply gas to the burner, the relay is actuated, opening the valve.
As a standard safety feature, the power supply to the valve relay driver circuit typically will include a power line which remains "on" only when a flame is present in the gas burner. This is to insure that gas does not flow to the burner when no flame is present.
However, in spite of this safeguard, in prior valve relay driver circuits, the failure or deterioration of at least one or more of some of the components in the driver circuit could result in the valve being inadvertently activated and opened, even when there was no burner flame.
Thus, one of the most critical elements of such a gas burner is the electrical circuit controlling the gas valve relay, which, as noted above, in turn controls the flow of gas to the burner. This circuit must never allow the relay to inadvertently pull in, which would open or maintain the gas valve open, due to a component failure, or else un-ignited gas might flow out of the system, causing a great safety hazard.
To achieve the level of safety required by the American Gas Association (AGA) and/or the manufacturer's guidelines, redundant circuits have often been required However, in the competitive environment of original equipment manufacturer (OEM) controls, the lowest cost is essential and yet redundancy is relatively expensive. Additionally, the level of redundancy is often difficult to predict, and the confidence in a new design's safety is always questionable if redundancy is the chief means of achieving safety.
To avoid these problems, the best method of achieving complete safety is for any failure of a component of the valve relay driver circuit to cause the driver circuit itself to become totally inoperable insofar as the valve relay is concerned, and that is the approach achieved in the present invention.
For general background information on gas burners and related circuitry and a gas-fired application thereof, reference is had to the following patents (there of course being many other patents relevant to the arts of relay controlled gas burners and gas-fired furnaces):
______________________________________ Patent No. Patentee(s) Issue Date ______________________________________ 4,034,235 Wade July 5, 1977 4,865,538 Scheele et al Sept. 12, 1989 ______________________________________
The Scheele et al patent, although having a different inventorship, is owned by the assignee hereof, and is not necessarily "prior art" to the present invention. Its disclosure, as well as the disclosures of the other of assignee's applications listed therein (Serial Nos. 095,508 & 095,506 both filed Sept. 10, 1987, being issued as U.S. Pat. No. 4,872,826 on Oct. 10, 1989 and U.S. Pat. No. 4,842,510 on June 27, 1989, respectively) are incorporated herein by reference.